 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.texteditor.spelling;

 import org.osgi.framework.Bundle;

 import org.eclipse.core.runtime.Assert;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IConfigurationElement;
 import org.eclipse.core.runtime.Platform;


 import org.eclipse.ui.internal.texteditor.spelling.EmptySpellingPreferenceBlock;

 /**
  * Describes an extension to the <code>spellingEngine</code> extension point.
  * <p>
  * This class is not intended to be subclassed by clients.
  * </p>
  *
  * @since 3.1
  */
 public class SpellingEngineDescriptor {

     /** Name of the <code>label</code> attribute. */
     private static final String LABEL_ATTRIBUTE= "label"; //$NON-NLS-1$
 /** Name of the <code>class</code> attribute. */
     private static final String CLASS_ATTRIBUTE= "class"; //$NON-NLS-1$
 /** Name of the <code>id</code> attribute. */
     private static final String ID_ATTRIBUTE= "id"; //$NON-NLS-1$
 /** Name of the <code>default</code> attribute. */
     private static final String DEFAULT_ATTRIBUTE= "default"; //$NON-NLS-1$
 /** Name of the <code>preferencesClass</code> attribute. */
     private static final String PREFERENCES_CLASS_ATTRIBUTE= "preferencesClass"; //$NON-NLS-1$

     /** The configuration element describing this extension. */
     private IConfigurationElement fConfiguration;
     /** The value of the <code>label</code> attribute, if read. */
     private String fLabel;
     /** The value of the <code>id</code> attribute, if read. */
     private String fId;
     /** The value of the <code>default</code> attribute, if read. */
     private Boolean fDefault;
     /** The bundle where this extension was defined. */
     private Bundle fBundle;
     /** <code>true</code> iff a preferences class has been specified */
     private Boolean fHasPreferences;

     /**
      * Creates a new descriptor for <code>element</code>.
      * <p>
      * This method is for internal use only.
      * </p>
      *
      * @param element the extension point element to be described.
      */
     public SpellingEngineDescriptor(IConfigurationElement element) {
         Assert.isLegal(element != null);
         fConfiguration= element;
     }

     /**
      * Reads (if needed) and returns the label of this extension.
      *
      * @return the label for this extension.
      */
     public String getLabel() {
         if (fLabel == null) {
             fLabel= fConfiguration.getAttribute(LABEL_ATTRIBUTE);
             Assert.isNotNull(fLabel);
         }
         return fLabel;
     }

     /**
      * Reads (if needed) and returns the id of this extension.
      *
      * @return the id for this extension.
      */
     public String getId() {
         if (fId == null) {
             fId= fConfiguration.getAttribute(ID_ATTRIBUTE);
             Assert.isNotNull(fId);
         }
         return fId;
     }

     /**
      * Creates a spelling engine as described in the extension's xml.
      *
      * @return the created spelling engine
      * @throws CoreException if the creation failed
      */
     public ISpellingEngine createEngine() throws CoreException {
         return (ISpellingEngine)fConfiguration.createExecutableExtension(CLASS_ATTRIBUTE);
     }

     /**
      * Returns <code>true</code> iff a preferences class has been
      * specified for this engine.
      *
      * @return <code>true</code> iff a preferences class has been
      * specified for this engine
      */
     private boolean hasPreferences() {
         if (fHasPreferences == null)
             if (fConfiguration.getAttribute(PREFERENCES_CLASS_ATTRIBUTE) == null)
                 fHasPreferences= Boolean.FALSE;
             else
                 fHasPreferences= Boolean.TRUE;
         return fHasPreferences.booleanValue();
     }

     /**
      * Creates a spelling preferences block as described in the extension's xml.
      *
      * @return the created spelling preferences block
      * @throws CoreException if the creation failed
      */
     public ISpellingPreferenceBlock createPreferences() throws CoreException {
         if (hasPreferences())
             return (ISpellingPreferenceBlock) fConfiguration.createExecutableExtension(PREFERENCES_CLASS_ATTRIBUTE);
         return new EmptySpellingPreferenceBlock();
     }

     /**
      * States whether the plug-in declaring this extension has been loaded already.
      *
      * @return <code>true</code> if the extension point's plug-in has been loaded, <code>false</code> otherwise.
      */
     public boolean isPluginLoaded() {
         if (fBundle == null)
             fBundle= Platform.getBundle(fConfiguration.getContributor().getName());
         return (fBundle != null && fBundle.getState() == Bundle.ACTIVE);
     }

     /**
      * Reads (if needed) and returns the default attribute value of this extension.
      *
      * @return the default attribute value for this extension.
      */
     public boolean isDefault() {
         if (fDefault == null) {
             String def= fConfiguration.getAttribute(DEFAULT_ATTRIBUTE);
             if ("true".equalsIgnoreCase(def)) //$NON-NLS-1$
 fDefault= Boolean.TRUE;
             else
                 fDefault= Boolean.FALSE;
         }
         return fDefault.booleanValue();
     }
 }
